Global Warming Could Trigger Photosynthesis Failure in Tropical Forests, Study Warns

A new study published in the journal Nature warned that tropical forests could suffer widespread leaf damage and death as a result of global warming.

The study, led by researchers from Northern Arizona University, used satellite and ground-based data to measure the temperature of leaves in the canopies of tropical forests around the world.

Global heating affects tropical forest leaves

The study found that the average temperature at which the photosynthetic machinery in tropical forest leaves begins to fail is about 46.7°C (116°F).

This temperature seems high, but it can be reached by leaves exposed to direct sunlight and low air humidity.

The researchers estimated that about 0.01% of all leaves in tropical forests are already experiencing temperatures above this limit.

The study also predicted that the proportion of leaves affected by overheating will increase exponentially with local warming.

Using a simple model based on experiments of warming plants, they calculated that once local temperatures increase by 4°C (7.2°F), which could happen under high-emissions scenarios, almost all leaves in tropical forests will die.

This would have devastating consequences for the structure and function of these ecosystems.

Tropical forest leaves are vulnerable to overheating

The study explained that tropical forest leaves are vulnerable to overheating because they have evolved to cope with relatively stable and humid conditions.

They also have limited ability to adjust their leaf temperature by changing their orientation, shape, or reflectance.

The study also suggested that overheating can trigger positive feedback loops that amplify the effects of warming.

Leaf death can reduce transpiration, which is the process of water evaporation from plant surfaces that cools the air, and can also lead to higher air temperatures and lower humidity, which in turn can increase leaf temperature and mortality.

Implications for tropical forest conservation and climate action

The study highlighted the importance of protecting tropical forests from global heating, as they provide vital ecosystem services such as biodiversity, water regulation, and climate moderation.

Tropical forests store about 25% of the world's terrestrial carbon and account for about 50% of global photosynthesis.

The study urged for urgent climate action to avoid high-emissions scenarios that could push tropical forests beyond their thermal limits.

The researchers noted that under low-emissions scenarios, most tropical forest leaves can avoid overheating and survive.

Tropical forest leaves adapt to climate warming

Tropical forest leaves are adapted to cope with relatively stable and humid conditions. They have little variation in their heat tolerance among species.

They also have limited ability to adjust their leaf temperature by changing their orientation, shape, or reflectance.

Plants can adapt their physiological mechanisms to deal with shifting environmental conditions through a process known as acclimation.

The capacity of plants to evolve new features that improve their fitness in response to shifting environmental conditions is known as adaptation.

Plants have the capacity to migrate to new areas that are more conducive to their survival and procreation.

These mechanisms can help tropical forest leaves survive global heating, but they also have limitations and costs.

Acclimation can only occur within a certain range of environmental variation and may reduce other aspects of plant performance.

Adaptation requires sufficient genetic variation and time for natural selection to occur. Migration depends on the availability and accessibility of suitable habitats and may face barriers such as human activities or geographic features.